This invention relates to a method for detecting image information which is capable of automatically detecting the image information of an original picture film such as a negative film out of pixel information of a frame segmented into pixels of predetermined areas.
In a photographic printing system, it is necessary to photographically measure density of an original film (e.g. a negative film) in order to determine the exposure amount or correction amount in photographic printing. In the prior art, the average density of a negative film is photographically measured in LATD (large area transmittance density) with photosensors such as photodiodes provided near the optical path in the optical system. The method of image detection using LATD is generally adapted to photographically measure a negative film, but not to measure image density of the film precisely and all over the frame. The method therefore often presents problems such as inaccurate determination of exposure amount or correction amount. When printing a negative film onto a sheet of photographic paper, it is necessary to change the exposure amount or the correction amount depending on the size of the film frame due to the difference in light diffusion. The size of an original film is visually discriminated, and inputted from a key board mannually in the prior art. Alternatively, the size of the film is discrminated by reading status signals of the negative film mounted on a negative film carrier. These operations, however, involve cumbersome key operation or signal processing resulting in frequent errors in input.
The present applicant has proposed a device shown in FIG. 1 in order to obviate such prior art defects (U.S. patent application Ser. No. 691,309). FIG. 1 shows one example of application of an image information detecting apparatus 10 in a conventional photographic printing system wherein a negative film 2 positioned on a negative film carrier 1 which has been conveyed to a printing section by a conveying mechanism 9 is illustrated with light from a light source 4 via color compensation means 3 of three complementary colors of yellow (Y), magenta (M) and cyan (C), and the light transmitted through the negative film 2 is directed to a sheet of photographic paper 7 via a lens unit 5 and a black shutter 6. The photographic paper 7 is coiled on a supply reel 7A, paid out and wound on a take-up reel 7B in synchronized movement with conveying or suspending movement of the negative film 2. Photosensors 8 such as photodiodes are provided near the negative film 2 on the side of the lens unit 5 detect image density information of red (R), green (G) and blue (B) or of the three primary colors. The detection signal from the photosensors 8 is used in photographic printing. The image information detecting apparatus 10 is provided near the negative film 2 at an angle from the optical axis LS of the light source 4 and the negative film 2. The apparatus houses a two-dimensional image sensor 11 comprising CCD (Charge Coupled Device) or MOS (Metal Oxide Semiconductor) and in front of the image sensor 11 is located a lens unit 12 which focuses substantially the center of the negative film 2. The image information detecting apparatus 10 is constructed as a unit having on the reverse side a substrate 13 which is packaged with a processing circuit of ICs (integrated circuits) and so on, for image processing.
The two-dimensional image sensor 11 comprises, as shown in FIG. 2, and image pickup section 101 for optically picking up an image, a storage section 102 for storing charges transmitted from the image pickup section 101, and an output register 103 for outputting the charges stored in the storage section 102. By controlling driving signals 101S through 103S from a driving circuit, the image information in two-dimensions (area) is photoelectrically converted and outputted serially from the output register 103 in the form of an analog image signal PS. The circuit mounted on the substrate board 13 has, for example, a circuit structure shown in FIG. 3. The image sensor 11 is driven by driving signals 101S through 103S supplied from the driving circuit 20. The light illuminating the image pickup section 101 of the image sensor 11 is outputted from the output register 103 as a picture signal PS, sampled and held by a sampled-and-hold circuit 21 at a predetermined sampling cycle. The sample value thereof is converted by an analog-to-digital (A/D) converter 22 into digital signals DS. The digital signals DS from the A/D converter 22 are inputted into a logarithmic converer 23 for logarithmic conversion, then converted to density signals DN, passed through a write-in control circuit 24 and finally written in a memory 25.
A reading speed signal RS from the driving circuit 20 is inputted into the write-in control circuit 24 in order to read out image information at a predetermined speed when the image sensor 11 is driven. The write-in control circuit 24 writes in the density signals DS at predetermined positions of a memory sequentially and correspondingly with the driving speed of the image sensor 11. In other words, the reading speed of the image sensor 11 is determined by the driving speed. The reading speed in turn determines the segmentation number of pixels in respect of an image area. The memory 25 should therefore store the detected information in correspondence with the number of pixels, too.
When a picture is printed in a conventional manner in the above mentioned structure, the light transmitted through one frame of the negative film 2 which has been conveyed to and standing still are at a printing position is detected by the photosensors 8. Then, the filters in the color compensation means 3 are adjusted in response to the picture signals for each of the primary RGB colors and the black shutter 6 is opened to expose a photographic paper 7 with the determined exposure amount.
According to this invention, on the other hand, an image information detecting apparatus 10 comprising a two-dimensional image sensor 11 of area scanning type such as a CCD is mounted at a position near the negative film 2 at an inclined angle in respect of an optical axis to facilitate mounting operation. The whole frame of the negative film 2 is segmented into a large number of arrayed pixels for detecting image information. In other words, when predetermined driving signals 101S through 103S are fed from the driving circuit 20 to the image sensor 11, the two-dimensional image sensor 11 is adapted to receive the light transmitted through the negative film 2 on the printing section via the lens unit 12. The two-dimensional image sensor 11 can therefore scan whole surface of a frame of the negative film 2 along the sanning lines SL1 sequentially by segmenting the whole area into a large number of small arrayed pixels as shown in FIG. 4A. After the whole area has been scanned, the output register 103 of the image sensor 11 outputs a picture signal PS sequentially, then the picture signal PS is sampled and held by the sampled-and-hold circuit 21 and the sampled value thereof is converted by the A/D converter 22 into digital signals DS. The digital signals DS from the A/D converter 22 are logarithmically converted by the logarithmic converter 23 to density signals DN. The density signals DN are controlled by the write-in control circuit 24 to be stored in a memory in the arrays corresponding to the pixels 2A shown in FIG. 4B and in terms of the density digital values of the negative film 2.
If the digital values for respective pixels of the negative film 2 or the density values for respective elements in respect of three primary colors are stored in the memory 25, it is possible to read out the digital values for any particular pixels of the negative film 2 out of the memory 25. If the density values for respective three primary colors of R, G and B are stored as shown in FIG. 4B, it is possible to read out such values from the memory for processing (which will be described hereinafter) in order to determine the exposure or correction amount for photographic printing in the same manner as in the prior art.
An elongated negative film 2 is conveyed consecutively frame by frame by a conveying mechanism 9 to a position on a negative film carrier 1. As shown in FIG. 5, a rectangular upper guide 1B having a frame aperture 1A is engaged with a lower guide 1C positioned therebelow in order to hold the negative film 2 therebetween for printing the film 2 frame by frame. The size of the aperture 1A of the upper guide 1B is completely identical with the size of a frame of a negative film 2 so that the peripheral portion of the frame without image or unexposed portion would not fall outside the area of the aperture 1A of the upper guide 1B. The area from which the two-dimensional image sensor 11 receives light is determined to correspond not only with one frame of the negative film 2 but also with a large sized film. The area includes the portion of the upper guide 1B where the light does not transmit. The image information of the area which the two-dimensional image sensor 11 detects becomes as shown in FIG. 6A in the case of a negative film carrier of 110 size while it becomes as shown in FIG. 6B in the case of the carrier of 135 size. FIGS. 6A and 6B show examples of detected image information of the unexposed portion (the developed film portion where no image is pictured) wherein the portion VA encircled by broken lines at the center defines the aperture 1A or the area of a frame. As the size of a frame corresponds to the size of a negative film 2, the size of an aperture 1A can be obtained by detecting the density "0" which means the transparent portion without image data read by the image sensor 11 and counting the area or the number. This leads to the discrimination of the size of a negative film 2. In this case, as the optical axis of the image sensor 11 is directed toward the substantial center of the aperture 1A, the size of the negative film 2 can be discriminated by counting the number of picture elements having the density "0" (or having the value close thereto) in hardware or software and comparing the counted value with a predetermined value for each size.
As described above, the size of the negative film 2 is determined by measuring the area of the density "0" and corresponds to the number of picture elements, which indicates the size of the aperture 1A of the negative film carrier 1. For example, as shown in FIG. 6A, if the number of picture elements of the density "0" is "32" (which may be 30 to 34 for allowance margin), the size is judged to be 110 size, as shown in FIG. 6B, if the number is "160" (which may be 156 to 164 for allowance margin), the size is judged to be 135 size, and if the number is "196" to "204", the size is judged to be 126 size. However, the method of size discrimination is not limited to the above method. The size information judged in the above manner is supplied to the photographic printing system so as to determine exposure amount by selection of applicable formula or by calculation with a formula for conducting photographic printing process in correspondence with the particular size.
In determining the exposure amount, the transmittance of the light of RGB color components over the whole area is controlled usually at a constant value so as to realize a print with balanced color and exposure. This is based on the empirical rule that the average reflectivity or transmittance of three colors obtained by integration of the whole scene, when an ordinary scene is photographed, is substantially constant. In other words, if a neutral object is exposed in a color negative film, the average LATD varies depending on the exposure amount, the quality of the light from a light source, the sensitivity of the RGB photo-sensitive layers of the color film, use of a mask, etc., but those variations can be controlled by making the printing exposure amount for R, G and B constant at the time of printing.
The variation in density of the three colors of a color film caused by the difference of color distribution of an objects, on the other band, cannot be controlled appropriately by the above mentioned method because the variation affects the area component ratio among the three colors. In the case where the composition in luminance is quite different from ordinary distribution, e.g. the one with extremely large area of high luminances or the one with large area of low luminance, the LATD cannot be properly controlled by the method of merely controlling the printing exposure amount with the average LATD because the variation in density on the negative film is caused by the area-wise variation of density of the object. Similarly, if the main object of a scene has the shadowed portion or extremely highlight portion compared with the surrounding objects, the density cannot be corrected as there are involved conditions extremely different from those preset in the printer. In order to solve such problems in determining printing exposure amount, there have been proposed methods as disclosed in Japanese Patent Laid-open No. 23936/1977, No. 28131/1979 or Japanese Patent Publication No. 2691/1981 which segment a frame of a negative film to obtain image information from each segmented portion, and determine the exposure amount which is appropriate to the scene from all the information obtained from respective segments. If it is assumed that the average LATD of a frame is represented by Da, the maximum density of segmented frame by Dmax and the minimum density by Dmin, the exposure amount X.sub.1 of a 135 F size film can be determined by the following equation: EQU X.sub.1 =a.sub.1 .multidot.Da+b.sub.1 .multidot.Dmax+c.sub.1 .multidot.Dmin+d.sub.1 ( 1)
The exposure amount X.sub.2 of a 110 size film can be determined by the following equation (2): EQU X.sub.2 =a.sub.2 .multidot.Da+b.sub.2 .multidot.Dmax+c.sub.2 .multidot.Dmin+d.sub.2 ( 2)
If a correction formula Xs like the one shown below is made available for each film size, any negative film can be printed with a proper exposure amount which has been properly corrected for the particular size.
Coefficients Ki and Kj are determined separately by experiments for each size, respectively. EQU Xs=Ki+Kj.multidot.x (3)
When exposure amount is determined or corrected with the information obtained from segments of a frame, there still remains a problem as to how to segment a frame. Another problem lies in that if segmentation method should vary depending on the size of the film, calculation process becomes complicated. In order to avoid such inconvenience, this invention enables to determine the exposure amount by means of segmentation techniques common to all sizes by one-to-one correspondence between the number of segmented areas and the position thereof. More particularly, the above equations (1) and (2) are united to obtain one common formula as follows: EQU X=a.multidot.Da+b.multidot.Dmax+c.multidot.Dmin+d (4)
Simultaneously, as shown in FIGS. 7A through 7E the size of the picture elements PX per se which are to be detected by the two-dimensional image sensor 11 is made constant for all the sizes: a frame of a 135 F size film shown in FIG. 7A is divided into 16 groups, i.e. by four columns into elements C1A through C4A horizontally and into two-column, three-column, two-column and three-column elements R1A through R4A vertically, and the frame central data is obtained from the central area CPA comprising 16 picture elements. In a 135 size film in FIG. 7B, a frame is divided into 16 groups by two horizontal columns into elements C1B through C4B and into two-column, three-column, three-column and two-column elements vertically R1B through R4B and the frame central data is obtained from the central area CPB comprising 16 picture elements. In a 126 size film shown in FIG. 7C, a frame is divided into 16 groups by 3 horizontal columns to the elements C1C through C4C and two-column, three-column, three-column and two-column elements vertically R1C through R4C and the frame central data is obtained from the central area CPC comprising 16 picture elements. Similarly, a frame of 110 size is divided into 16 groups each of which comprises two horizontal columns and one vertical column (C1D through C4D horizontally and R1D through R4D vertically) and the central area CPS comprises four picture elements. The disk size film of FIG. 7E is divided into 16 groups by segmenting a frame into two-column, one-column, one-column and two-column elements horizontally C1E through C4E and by one vertical column R1E through R4E and the central area CPE comprises four picture elements. In this manner, all the frames of respective film sizes are divided into 16 groups E1 through E16 of segments and all the central area CPA through CPE are defined to include the center of the frame to obtain image information. It is therefore not necessary to change reading-out area of the image sensor for various film sizes. with only one common equation, a frame can be processed for any film size. One segment area may comprise plural elements; however, it is possible to obtain image information of each segmented area simply by calculating a mean value of each element data. As the frames of respective film sizes comprise area groups E1 through E16 and the central areas CPi (i=A through E), and as the average information of respective area groups E1 through E16 and CPi can be easily calculated from the data of component elements, the exposure amount X can be obtained by using the above formula (4) and the obtained exposure amount X can be corrected properly by the above formula (3), even if the size of each negative film conveyed to the printing section varies.
However, in the above mentioned embodiments, the two-dimensional image sensor 11 receives light at a constant magnification ratio irrespective of the size of the negative film frame. Although this equalizes the size of the images in relation to pixels of the two-dimensional image sensor 11, the size of the light receiving area on the image sensor inconveniently changes with a wide margin depending on the size of the negative film 2. As described in relation to FIGS. 7A through 7E, it becomes necessary to classify image information which widely differs from size to size to enable use of one common printing exposure expression. The conditions in detection of image information of the negative film 2 changes as mentioned above depending on the size of the film frame. This presents a problem especially in the case of a small size film because the number of its effective pixels is small to lower the resolution. This often incapacitates the device to perform sufficient processing.